Added a new event listener implementation responsible for auto-saving
file-based configurations.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1462198 13f79535-47bb-0310-9956-ffa450edef68
FileBasedConfigurationBuilder now supports an auto save mode.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1462199 13f79535-47bb-0310-9956-ffa450edef68